Process for obtaining smooth surfaces of metal ingots made by chill casting



United States Patent 3,362,464 PROCESS FOR OBTAINING SMOOTH SURFACES 0F METAL INGOTS MADE BY CHILL CASTING Alfred Theis, Burgsolms, Manfred Reiher, Hofheim, Taunus, and Heinrich Anger, Frankfurt am Main, Germany, assignors to Farhwerke Hoechst Aktieugesellschaft vormals Meister Lucius & Bruning, Frankfurt am Main, and Edetstahlwerke Buderus AG. (vormals Stahlwerk Rockling-Buderus AG), Wetzlar, Germany No Drawing. Filed May 18, 1965, Ser. No. 456,859 Claims priority, application Germany, May 21, 1964,

7 Claims. cl. 16455) ABSTRACT OF THE DISCLOSURE The present invention relates to a process for obtaining smooth surfaces of metal ingot-s, particularly of iron or steel ingots, made by chill casting.

It is known that the inner walls of ingot molds used for casting metals, particularly iron and steel, can be provided, before casting the ingots, with a coating to obtain ingots having fairly smooth surfaces. For this purpose, a lacquer or varnish coating may, for example, be used or a layer of very finely divided carbon in the form of soot may be applied to the inner wall of the mold with the help of an acetylene flame. The application of liquid lacquers or varnishes is not only complicated but yields also layers of irregular thickness and thus easily gives rise to pore formation in the surfaces of the ingot. The formation of a soot layer with the help of acetylene involves considerable dangers to the attendants and can be applied only in the case of small ingot molds. When the liquid material to be cast is introduced into the ingot molds, a casting foam forms on the bath surface. The foam rises with the rising bath level and deposits on the walls of the ingot mold, thus causing overboiling. To obtain ingots having satisfactory surfaces, deposition of casting foam on the walls of the ingot molds must be prevented from the first.

For degassing, it has been proposed to add polytetrafiuoroethylene to steel melts. In this case, however, gaseous degradation products are formed which are very injurious to the health of the attendants.

Now We have found that smooth surfaces of metal ingots, particularly iron or steel ingots, made by chi-ll casting can be obtained by adding granular chlorinated high molecular weight plastic substances, advantageously in admixture with a flux, to the melt before and/or during casting.

As chlorinated high molecular weight plastic substances it is advantageous to use polyvinyl chloride, copolymers of vinyl chloride, advantageously with vinyl acetate, polyvinylidene chloride, chlorinated polyolefins and mixtures of these polymers. Mixtures of polyvinyl chloride with to 30%, calculated on the mixture, of chlorinated polyethylene are particularly advantageous.

High molecular weight chlorinated parafiins may, however, also be used as additives in the process of the invention.

The high molecular weight plastic substances are advantageously added in an amount within the range of 5 1 to 50 grams, preferably to 25 grams, per ton of metal.

To render the casting foam fluid, the additives may advantageously be used in admixture with a common flux, for example fluorspar, or other fluorides of metals of 10 Groups I to III of the Mendelyeevs Periodic Table, the

flux being advantageously used in an amount of up to 80% calculated on the mixture.

The granular high molecular Weight plastic substances or their mixtures with a flux, which can easily be added in controlled amounts, are degraded at the high temperature of the material to be cast and form carbon deposits in a very finely divided form between the melt and the wall of the mould, thus protecting the wall of the mold and improving the surface of the ingot. Furthermore, removal from the mold of the cooled ingot is facilitated. In the manufacture of metal ingots, particularly iron or steel ingots, the process of the invention can be used for bottom casting and particularly for top pouring and yields ingots having satisfactory smooth and uniform surfaces.

As compared with other known substances used for the same purpose, the high molecular weight substances used as additives in accordance with the invention have the advantage that they are flame-resistant and that the vapors developed by their degradation are not so injurious to health as those of fiuorinated polymers, for example polytetrafluoroethylene.

We claim:

1. In the process for the manufacture of metal ingots having a smooth surface by casting a liquid metal melt into an ingot mold, the improvement which comprises adding to the liquid metal melt a chlorine containing high molecular weight plastic substance selected from at least one compound of the group consisting of polyvinyl chloride, copolymcrs of vinyl chloride with vinyl acetate, 4 polyvinylidene chloride and a chlorinated polyethylene in granular form.

2. In the process for the manufacture of ingots made of a metal selected from the group consisting of iron and steel, having a smooth surface by casting a liquid metal melt into an ingot mold, the improvement which comprises adding to the liquid melt a chlorine containing high molecular weight plastic substance of polyvinyl chloride and a chlorinated polyethylene in granular form.

3. The process of claim 2 which comprises adding to the liquid metal melt a mixture of a chlorine containing high molecular weight plastic substance of polyvinyl chloride and chorinated polyethylene and up to 80%, calculated on the mixture, of a calcium fluoride fl-uxing agent in granular form.

55 4. The process of claim 2, wherein 1 to 50 g./t. of the chlorine containing high molecular weight plastic substance is added to the liquid metal melt.

5. The process of claim 2, wherein 10 to 25 g./t. of the chlorine containing high molecular weight plastic sub- 50 stance is added to the liquid metal melt.

'6. In the process for the manufacture of metal ingots having a smooth surface by casting a liquid metal melt into an ingot mold, the improvement which comprises adding to the liquid metal melt a mixture of polyvinyl 65 chloride and 5 to 30%, calculated on the mixture, of a chlorinated polyethylene, said mixture being in granular form and a fluxing agent admixed therewith.

7. In the process for the manufacture of metal ingots having a smooth surface produced by chill casting said 7 ingots, the improvement comprising adding to a liquid metal melt a mixture of (a) a polyvinyl chloride, (b) 5 to 30% of a chlorinated polyethylene on basis of the 3 4 total chlorine containing components, and (c) up to 80% 3,153,826 10/1964 Horton 164-26 of calcium fluoride on basis of the total chlorine con 3,194,695 7/1965 Yanagawa 164-67 taining components, said mixture being in a granular 3,212,145 10/1965 Green 16467 form. 3,216,078 11/1965 Zrimsek 164-56 References Cited 5 FOREIGN PATENTS UNITED STATES PATENTS 655,755 1/1963 Canada. 1,889,905 12/1932 Saeger.

3,023,119 2/1962 Anderson a a1 J. SPENCER OVERHOLSER, Primary Examiner. 3,035,318 5/1962 Campbell 164--72 m V. K, RISING, Assistant Examiner. 

